Implantation mask formation

Abstract

Implantation mask formation techniques described herein include increasing an initial aspect ratio of a pattern in an implantation mask by non-lithography techniques, which may include forming a resist hardening layer on the implantation mask. The pattern may be formed by photolithography techniques to the initial aspect ratio that reduces or minimizes the likelihood of pattern collapse during formation of the pattern. Then, the resist hardening layer is formed on the implantation mask to increase the height of the pattern and reduce the width of the pattern, which increases the aspect ratio between the height of the openings or trenches and the width of the openings or trenches of the pattern. In this way, the pattern in the implantation mask may be formed to an ultra-high aspect ratio in a manner that reduces or minimizes the likelihood of pattern collapse during formation of the pattern.

What is claimed is: 
     
       1. A method, comprising:
 forming a trench in a photoresist layer; 
 performing a resist hardening operation on the photoresist layer to cause a hardening layer to form on a top surface of the photoresist layer and on sidewalls of the trench; and 
 performing, after performing the resist hardening operation, an ion implantation operation to form an isolation well in a substrate using the trench as an implantation mask. 
 
     
     
       2. The method of  claim 1 , wherein forming the trench comprises:
 forming the trench to a width in range of 200 nanometers to 260 nanometers. 
 
     
     
       3. The method of  claim 1 , wherein forming the trench comprises:
 forming the trench to a height in range of 1 micron to 2 microns. 
 
     
     
       4. The method of  claim 1 , wherein forming the trench comprises:
 forming a plurality of trenches, including the trench, in a grid pattern. 
 
     
     
       5. The method of  claim 1 , wherein forming the trench comprises:
 exposing the photoresist layer to a radiation source; and 
 removing an exposed portion or a non-exposed portion of the photoresist layer. 
 
     
     
       6. The method of  claim 1 , wherein performing the resist hardening operation on the photoresist layer comprises:
 performing a surface treatment operation on the top surface and on the sidewalls using a perfluorinated compound. 
 
     
     
       7. The method of  claim 1 , wherein the hardening layer is formed to have a thickness in range of 10 nanometers to 30 nanometers. 
     
     
       8. The method of  claim 1 , wherein an aspect ratio, between a height of the trench and a width of the trench, is greater than or equal to 10 based on formation of the hardening layer. 
     
     
       9. The method of  claim 1 , wherein an aspect ratio, between a height of the isolation well and a width of the isolation well, is greater than or equal to 10. 
     
     
       10. The method of  claim 1 , further comprising:
 removing the photoresist layer and the hardening layer after performing the ion implantation operation. 
 
     
     
       11. A method, comprising:
 forming a plurality of trenches through a photoresist layer over a substrate; 
 forming a hardening layer by performing a surface treatment operation on one or more top surfaces of the photoresist layer and on sidewalls of the plurality of trenches; and 
 forming isolation wells in the substrate by performing, after forming the hardening layer, an ion implantation operation using the photoresist layer and the plurality of trenches as an implantation mask. 
 
     
     
       12. The method of  claim 11 , wherein performing the surface treatment operation comprises:
 depositing a perfluorinated compound onto the top surfaces of the photoresist layer and on the sidewalls of the plurality of trenches by a plasma enhanced chemical vapor deposition (PECVD) operation. 
 
     
     
       13. The method of  claim 11 , wherein forming the hardening layer increases an aspect ratio, between a height of the plurality of trenches and a width of the plurality of trenches, to be equal to or greater than 10. 
     
     
       14. The method of  claim 11 , wherein performing the surface treatment operation comprises:
 performing the surface treatment operation for a duration in a range of 30 to 120 seconds. 
 
     
     
       15. The method of  claim 11 , wherein forming the isolation wells comprises:
 forming the isolation wells to an aspect ratio, between a height of the isolation wells and a width of the isolation wells, is greater than or equal to 10. 
 
     
     
       16. The method of  claim 11 , further comprising:
 forming one or more photodiodes in the substrate between the isolation wells. 
 
     
     
       17. A method, comprising:
 forming a plurality of trenches through a photoresist layer over a substrate to an initial aspect ratio between a height of the plurality of trenches and a width of the plurality of trenches; 
 increasing, after forming the plurality of trenches, the initial aspect ratio by performing a resist hardening operation; 
 performing, after increasing the initial aspect ratio and using the photoresist layer, an ion implantation operation to form a plurality of isolation wells in the substrate; 
 forming, in between the plurality of isolation wells, a plurality of photodiodes; 
 forming a plurality of color filter regions over the plurality of photodiodes; and 
 forming a micro-lens layer over the plurality of color filter regions. 
 
     
     
       18. The method of  claim 17 , wherein performing the resist hardening operation comprises:
 forming a carbon-based crust on sidewalls of the plurality of trenches. 
 
     
     
       19. The method of  claim 17 , wherein performing the resist hardening operation comprises:
 forming a hardening layer having a thickness in a range of 10 nanometers to 30 nanometer. 
 
     
     
       20. The method of  claim 17 , further comprising:
 forming a grid structure above substate after forming the plurality of photodiodes; and 
 wherein forming the plurality of color filter regions comprises:
 forming the plurality of color filter regions in openings of the grid structure.